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mtbengg
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Join Date: Aug 2009
Posts: 6

Simple Braking Mechanism for Cable and Pulley

11/03/2009 12:53 PM

Hello,

I am looking for some help on a project I'm working on. I've been trying to brainstorm a solution but I'm having troubles coming up with something cost effective.

I have shuttle on a vertically mounted linear rail. It is attached to a spring, via a cable and pulley. The shuttle needs to be able to move up and down to accommodate different length units that go on the shuttle. The spring is there to pull the unit up once it is loaded and also to allow the shuttle to move down to assist loading.

Once the unit is loaded, it needs to lock in place to allow the machine to run it's cycle. There is no more than 200lbs of downward force. The original machine designer had a pneumatic cylinder that fired a couple of bicycle brake pads against the linear rail, but the pads slip under the load.

I am trying to think of way to allow to lock the shuttle by using the cable and/or pulley. My feeling though is that cable will slide on the pulley if the pulley is locked.

So, to sum it up, the problem is to allow the cable to move freely until the PLC signal tells it to lock in place. The cable runs vertically up to the pulley and does a 180 back down to attach to the spring.

Thoughts?
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BiomedWV
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#1

Re: Simple Braking Mechanism for Cable and Pulley

11/03/2009 1:44 PM

Have you thought about using a magnetic lock?
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mtbengg
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#2
In reply to #1

Re: Simple Braking Mechanism for Cable and Pulley

11/03/2009 2:02 PM

I had not. I did a quick search on the interwebs and it seems that most are related to doors. I'd be looking for something that is smaller than the ones which are intended for doors.

Do you know of a source of non-door magnetic locks?
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Doorman
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#4
In reply to #2

Re: Simple Braking Mechanism for Cable and Pulley

11/03/2009 3:02 PM

Well, if a magnetic lock did not lock some sort of door, what would it lock?

I believe BiomedWV has a pretty good idea. To follow your thought about magnet door locks: Size of the large one is 12" X 3" X 1-3/4", they are available with up to 1,800 lbs (816 Kg) of direct bond, and draw only 4 watts (24VDC). While this 1,800 lbs rating is certainly not accurate in shear, use two. They are not very expensive, have sealed electronics, UL listed (for doors, anyway)... this is turning into a sales pitch. Sorry.

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Randall
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#11
In reply to #2

Re: Simple Braking Mechanism for Cable and Pulley

11/04/2009 3:56 AM

magswitch

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lyn
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#3

Re: Simple Braking Mechanism for Cable and Pulley

11/03/2009 2:03 PM

You might try modifying a jumar with a cylinder to release it.

Don't know what happened to the pictures. Click on the little squares.
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Anonymous Poster
#5

Re: Simple Braking Mechanism for Cable and Pulley

11/03/2009 3:23 PM

Try self energized band brake, you may need to install another pulley on the shaft next to the original pulley for band brake. look for the design of band brakes in any machine component design book or on the web.
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ozzb
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#6

Re: Simple Braking Mechanism for Cable and Pulley

11/03/2009 4:08 PM

You did not specify what type of linear rail you have but this company make a brake for linear rails. pneumatic or electrically actuated. Holding force of 350 lbs.

http://www.nexengroup.com/nexen/index.jsp

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lyn
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#7
In reply to #6

Re: Simple Braking Mechanism for Cable and Pulley

11/03/2009 4:11 PM

I like your idea better.
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ozzb
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#13
In reply to #7

Re: Simple Braking Mechanism for Cable and Pulley

11/04/2009 1:45 PM

Thanks Lynch

And to answer your question it's so the bureaucrats can get a few more holes of golf in before it get dark.

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mike k
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#8

Re: Simple Braking Mechanism for Cable and Pulley

11/03/2009 10:10 PM

Take an extra wrap around the pulley and the wire won't slip. You may have to use a wider pulley so the cable doesn't get lapped over itself. Since you have a spring in the device, the cable will always be tight, right? The brake is inside the pulley. You can use a motorcycle front wheel hub for the pulley...hydraulic brakes on the new ones.

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bwire
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#9

Re: Simple Braking Mechanism for Cable and Pulley

11/03/2009 11:49 PM

I've used disc brake caliper assy on similar projects, sometimes those from motorcycles are perfect.

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LG_Dave
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#10

Re: Simple Braking Mechanism for Cable and Pulley

11/04/2009 1:35 AM

The original brake pads and pneumatic cylinder should have been sized to hold the working load. Take a little time to review the cylinder pressure, linkage to the pads and the pad dimensions.

Has the cylinder pressure changed?

Has the linkage worn or bent?

Have the pads worn or become contaminated?

You may find it more productive to restore the functionality that was originally designed in.

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suresh sharma
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#12

Re: Simple Braking Mechanism for Cable and Pulley

11/04/2009 7:23 AM

I suggest you to install 100 kg Chain Electric Hoist. Hoist can be fitted with limit switches to stop at particular height like passenger lift. I hope shuttle has its own dead weight for lowering down. Also there is space on the top for fixing the Hoist. You have not indicated the length of travel hoisting speed.

Suresh Sharma.

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Users who posted comments:

Anonymous Poster (1); BiomedWV (1); bwire (1); Doorman (1); LG_Dave (1); lyn (2); mike k (1); mtbengg (1); ozzb (2); Randall (1); suresh sharma (1)

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